For the following set of cash flows, Year Cash Flow $-$$$7,8005,5003,4004,700$ a $.$ What is the NPV at a discount rate of $0$ percent? b$.$ what is the NPV at a discount rate of $10$ percent? c$..$ What is the NPV at a discount rate of $18$ percent? d$.$ What is the NPV at a discount rate of $23$ percent?